The invention set forth in this specification pertains to new and improved perforate roof drain covers for use on flat or essentially flat roofs which are covered with comparatively small particles of gravel of other inorganic materials.
Flat or nearly flat roofs commonly used are frequently covered with comparatively small inorganic particles so as to protect the organic materials in the roof from deterioration cause by actinic light and, in some cases, for other reasons. Although on occassion such particles may to at least a degree be bonded in place they are usually merely scattered on a roof so as to be held in place by gravity. Although this is usually satisfactory since the weight the particles keeps them in place, at times, it is not satisfactory because, during heavy rains or the like, the flow of water on a roof will tend to move such particles toward and into the drain or drains used to prevent water from accumulating on a roof to such an extent that there is a possibility of structural or other damage.
Although such drains can be constructed in many different ways, they are frequently constructed so as to use a centrally located pipe of pipe section extending downwardly from a funnel like transition area having an outwardly extending flange located at its open end. The transition area is normally covered by a screen or related perforate member designed to preclude the entrance of any material other than water into the pipe or pipe section. These screens or related members can be and are commonly referred to as "grates". They can be constructed in many different ways. Such grates are normally designed to act as perforate barricades, which will hold back any debris from passage through the drain.
Such drains are normally installed so that the flange lays in a recess in the roof so as to support the drain and so that the pipe section is connected to an appropriate sewer line. Normally the flange is covered with or bonded to the material in a roof so that any water on the roof will not get under the flange but instead will flow through the drain. Drains or drain structure of this category are shown in the Logsdon U.S. Pat. Nos. 3,884,809 entitled Scupper Drain Structure and 4,487,690 entitled Sump Or Flush Installable Roof Drain. Several known screen type perforate members are indicated in the Logsdon U.S. Pat. Nos. 4,400,272 entitled Drain Grate With Adjustable Weirs and 4,525,273 which is also entitled Drain Grate With Adjustable Weirs.
Because of the manner in which such drains are constructed, all sorts of debris can easily accumulate within them. As this occurs they are apt to become either completely or partially stopped up. This is undesirable because of the possibility of roof damage. Both organic items such as leaves and scrap paper and various inorganic particles will normally tend to accumulate, causing drains on gravel or similarly covered flat or nearly flat roofs to stop up. However, in studying the tendency of such drains to stop up it has been noticed that such organic and inorganic materials tend to "act" differently in causing a drain stoppage.
Because such inorganic particles usually or normally are somewhat heavier than leaves and related organic materials, they tend to move generally along the surface of a roof and to accumulate in the general region around the base of the perforate member or grate while the organic materials tend to "float" over these inorganic particles so as to accumulate on top of them against the grate. As a result of this, there will be a tendency for the particles to form a somewhat perforate ring around base of the perforate member or grate.
This grate will then tend to act more or less like a leaky dam so as to cause leaves and the like to float higher and higher. Concurrently organic materials will pile up on or accumulate within this ring against the grate so as to decrease its permeability. All of this will have the effect of making it more difficult for water to drain from a roof. As a result, there will be a tendency for the water to accumulate on the roof more or less as water tends to accumulate in back of a dam before flowing over the dam. As this occurs, the danger of damage resulting from the weight of the water accumulation increases.
It will be realized that this is something of any oversimplification of what actually occurs at and adjacent to a roof drain during a heavy rain when loose inorganic particles and leaves, paper and other related materials are present. However, it effectively indicates that there is a need for improved roof drain covers--more specifically-roof drain coversm which are designed and constructed so as to minimize the chances of accumulations adjacent to or against a roof drain screen or grate causing a siginificant body of water from accumulating on a roof.